Q. I’m a plumber, and during a recent meeting with a customer, I noticed that they were using treated lumber indoors, including for beams. One of the beams was a steel plate beam. I told the owner it might not be safe to use green-colored treated lumber inside the house. Do you agree?
A. Yes, I agree. Pressure-treated lumber, intended for outdoor use, can be dangerous, but the beam with the steel plate is also a problem. There’s a reason that when you go to a big-box store or lumberyard, the lumber is separated into two areas, treated and untreated. There’s also a reason the big-box stores stopped letting customers cut treated lumber in the store.
Pressure-treated lumber, developed over 100 years ago, was created by forcing chemicals into lumber using giant pressure chambers. Treatment was intended to keep lumber from being eaten by microbes, insects and termites, and it has worked well, but with unintended consequences. The poisons used in the lumber were studied and shown to cause respiratory ailments, and in some cases, repeated or prolonged contact led to skin cancer. Although poison formulas have been changed to be safer, imagine getting a splinter from the local playground jungle gym. It’s easy to understand why school systems across the country replaced the outdoor play equipment with plastic, steel and painted products.
The best place for treated lumber in a building is the closest to where most insects can enter, near the ground. The base plates that connect the floors to the foundation are usually treated lumber, along with an expandable foam and a copper or plastic rigid sheet called a termite shield. If the materials are installed correctly, the invaders can’t get into the house. Because the base plate is generally covered with other materials or in a place that isn’t as occupied, it’s safer than in the general living spaces above.
The steel-to-wood connection is dangerous for the separate reason that the chemicals used to treat lumber are very corrosive to metal, to the point that a steel plate inserted between two pieces of lumber to form what’s called a “flitch plate beam” could actually corrode and weaken to collapse in only a few years after it was made.
Since lumber used for decks is generally treated lumber for outdoor use, it is mostly recommended for the structural parts underneath, and not the exposed parts. Outdoors, the off-gassing of poisons used to treat the lumber is most often not considered harmful, although highly sensitive people may still be affected. I haven’t read specific studies on this, but understand that the use of poisons and pesticides outdoors can still have a profound effect on those people. So use gloves when handling treated lumber, don’t use it indoors and coat or cover the exposed lumber, especially in areas where food will be served. Good luck!
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